1. Field of the Invention
The present invention relates to an industrial robot including a guiding mechanism for guiding a cable connected with an end effecter.
2. Description of the Related Art
FIG. 15 is a diagram showing an industrial robot as a related art. This industrial robot includes a wrist mechanism having three joint portions 11, 12, 13. Each of the joint portions 11, 12, 13 is constructed by using a reduction device-integrated type motor into which a reduction mechanism is integrally incorporated.
The first joint portion 11 is provided at an arm 8 and is configured to rotate a first rotating portion 1 about a first axis L11. The second joint portion 12 is provided at a first fixed portion 2 fixed to the first rotating portion 1 and is configured to rotate a second rotating portion 3 about a second axis L12 relative to the first fixed portion 2. The third joint portion 13 is provided at a second fixed portion 4 fixed to the second rotating portion 3 and is configured to rotate a third rotating portion 5 about a third axis L13 relative to the second fixed portion 4. An end effecter is fixed to the third rotating portion 5.
The second axis L12 extends perpendicularly to the first axis L11. The third axis L13 extends perpendicularly to the second axis L12. When the first to third joint portions 11 to 13 rotate the corresponding rotating portions 1, 3, 5 by predetermined rotational amounts respectively, the end effecter can be moved to any given position within a movable range relative to the arm 8.
Each of the first joint portion 11 and third joint portion 13 is formed into a hollow shape. The second joint portion 12 is located at a position apart from the first axis L11. In such a configuration, a cable extending through the arm 8 up to the end effecter will be inserted through the first joint portion 11 and third joint portion 13 while bypassing the second joint portion 12. Thus, extension of the cable around the outer periphery of the wrist mechanism can be prevented. This type of industrial robot is disclosed in JP 2005-14103 A.
If the third joint portion 13 is positioned unduly close to the second axis L12, the curved cable will interfere with the third joint portion 13 upon rotating the third joint portion 13 about the second axis L12. Accordingly, in order to prevent such interference between the cable and the third joint portion 13, the third joint portion 13 should be spaced away from the second axis L12 along the axial direction of the third axis L13. In such a related art described above, since the third joint portion 13 is constructed by using a reduction device-integrated type motor, it should be larger in size in the third axial direction by the motor provided thereto, as compared with the case using the reduction device alone. Therefore, in the related art, the third joint portion 13 should be spaced away a significantly greater distance from the second axis L12.
When the distance that the third joint portion 13 is spaced away from the second axis L12 is increased, the distance from the second axis L12 to the end effecter is also increased. In such a case, the torque required for rotating and driving an end effecter by using the first joint portion 11 and second joint portion 12 should be increased. This is problematic. Also, in such a case, if the weight of the end effecter is significantly large, high speed driving of the end effecter will be difficult, or otherwise downsizing of the first joint portion 11 and/or second joint portion 12 may tend to be difficult. Similar problems may also occur in the case where an object to be moved other than the end effecter is fixed to the third rotating portion 5 of the third joint portion 13.